ISTANBUL, May 6 (Reuters) - The United States and European Union have expressed deep concern over Turkey's plans for offshore drilling operations in an area claimed by Cyprus as its exclusive economic zone, adding to tensions between Ankara and its Western allies.

The statements at the weekend came after Turkish Foreign Minister Mevlut Cavusoglu said "we are starting drilling" in the region.

Turkey and the internationally recognized Greek Cypriot government have overlapping claims of jurisdiction for offshore oil and gas research in the eastern Mediterranean, a region thought to be rich in natural gas.

"The United States is deeply concerned by Turkey's announced intentions to begin offshore drilling operations in an area claimed by the Republic of Cyprus as its Exclusive Economic Zone," State Department spokesperson Morgan Ortagus said on Sunday.

"This step is highly provocative and risks raising tensions in the region. We urge Turkish authorities to halt these operations and encourage all parties to act with restraint."

Cavusoglu said that Turkish seismic research vessel Barbaros Hayrettin Pasa was continuing work in the region.

"We will conduct drilling in areas of Turkey's continental shelf and we are starting our drilling work at points identified by Barbaros Hayrettin Pasa," he said in northern Cyprus on Saturday.

The Cyprus foreign ministry said it "strongly condemns" Turkey's drilling operations within its exclusive economic zone.

"This provocative action by Turkey constitutes a flagrant violation of the sovereign rights of the Republic of Cyprus," it said on Saturday.

Turkey's foreign ministry said on Monday that Ankara was defending Cypriot Turks' rights and would continue to do so as long as it said Greek Cypriots excluded them from decision-making and carried out unilateral hydrocarbon activities.

"The USA making a call to Turkey...is an approach which is neither constructive nor in line with international law," it said, adding that it was "unacceptable for third parties to literally put themselves in the place of international courts."

URGENT EU CALL

The U.S. statement followed similarly worded comments on Saturday by EU foreign policy chief Federica Mogherini, who expressed "grave concern" about Turkey's intentions.

"We urgently call on Turkey to show restraint, respect the sovereign rights of Cyprus in its exclusive economic zone and refrain from any such illegal action to which the European Union will respond appropriately and in full solidarity with Cyprus."

Any escalation between Turkey and the United States could put more pressure on relations already strained on several fronts, including missile defense and military operations in Syria.

Cavusoglu said in February that Turkey would soon begin drilling for oil and gas near Cyprus. Ankara launched its first drill ship in October off the coast of Turkey's southern Antalya province.

The ship was located 70 km (45 miles) off the west coast of Cyprus on Monday, Refinitiv Eikon shipping data shows.

Breakaway north Cyprus, which is supported by Turkey, says that any offshore wealth also belongs to them, as partners in the establishment of the Republic of Cyprus in 1960.

The island was divided in 1974 after a Turkish invasion triggered by a brief Greek-inspired coup. Countless peacemaking endeavors have failed and offshore resources have increasingly complicated peace negotiations. (Additional reporting by Tuvan Gumrukcu, Can Sezer and Michele Kambas Writing by Daren Butler Editing by Dominic Evans, Louise Heavens and David Goodman)